Since an organic light emitting diode emits light directly from a light emitting layer located between a cathode and an anode, there is an advantage that there is no need for a backlight, the expression range of light is wider than that of a Liquid Crystal Display (LCD), and a black level is excellent. That is, when a voltage is applied to the cathode and the anode in the organic light emitting diode, electrons and holes are injected from each electrode, and the injected electrons and holes pass through an electron transport layer and a hole transport layer to couple the electrons and holes in the light emitting layer.
A light emitting material of the light emitting layer is excited by the energy due to the coupling, and light is generated when the light emitting material returns from the excited state to a ground state again. The light emitted when returning from the excited state (singlet state) to the ground state is fluorescence, and the light emitted when returning from the singlet state to the ground state via a triplet state which has a somewhat low energy level is phosphorescence. The energy that can not be used with light even in the excited state may be inactivated without being emitted.
In the organic light emitting diode, a metal thin film such as aluminum, a silver-magnesium alloy or calcium may be used for the cathode, and a transparent metal thin film such as indium tin oxide called ITO may be used for the anode. An organic compound layer formed between the cathode and the anode may include a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). When a driving voltage is applied between the cathode and the anode, holes passing through the hole transport layer (HTL) and the electrons passing through the electron transport layer (ETL) move to the emission layer (EML) to form excitons, and as a result, the emission layer (EML) generates visible light. The generated light is reflected on a reflection surface and passes through the transparent electrode and a substrate (a glass plate, a plastic plate, etc.).
The organic light emitting diode may be classified into a passive matrix organic light emitting diode (PMOLED) and an active matrix organic light emitting diode (AMOLED) according to a control method thereof.
The PMOLED has a disadvantage in that a voltage is applied to a horizontal axis and a vertical axis of a light emitting device arranged on a screen, respectively, to illuminate an intersection thereof, so that the structure is relatively simple and the production cost is low, but a sophisticated screen may not be realized. The AMOLED is intended to overcome the shortcomings of the PMOLED, and there is an advantage of embedding a thin film transistor (TFT) in each light emitting device so that each device can be individually controlled to emit light. In recent years, since the screen size may be applied to a large device, its application range is widened.
Although Korean Patent Registration No. 10-1170806 discloses a device for a passive matrix, specifically, there is not disclosed a method for implement illuminance sensing and touch sensing in the PMOLED.